Conventional standing post tire curing presses typically comprise a bladder assembly and a tire mold assembly. The bladder assembly typically has a bladder, a standing center press post and upper and lower clamp ring assemblies that clamp the tire and oppose each other so as to support both sides of the tire. By way of definition, "opposing clamp ring assemblies" is understood to mean clamp ring assemblies that are opposite each other along the center post. The upper clamp ring assembly includes an upper mold ring and an upper clamp ring. The lower clamp ring assembly includes a lower bead ring and a lower clamp ring.
In a conventional tire curing process, the bladder clamp ring assemblies and spacer are moved relative to each other and pressure or vacuum is applied depending upon the point in the tire curing process. First, a loader loads a green tire assembly over the center post of the bladder assembly so that the lower tire bead is adjacent to the lower bead ring with the upper clamp ring assembly raised up to its fully extended position, also known as the "primary stacking height", and with a vacuum being applied to the bladder. Typically, the upper clamp ring assembly is fixed to the center post utilizing a collar. Thus, to raise the upper clamp ring, the center post is extended from the well.
Once the green tire assembly is loaded, the vacuum is typically broken and the upper clamp ring is dropped on a fixed-height spacer. The point to which the upper clamp ring is dropped to rest on the spacer is known as the "secondary stacking height." A shaping pressure is applied to pre-shape the tire. The tire loader will release after the tire is preshaped. Then the tire mold assembly is closed around the green tire and the spacer travels further down the center post to the well.
During unloading of the cured tire, the bladder assembly is raised up along the center post so that stripping arms may be inserted adjacent to the lower bead ring and side wall of the tire. As the stripping arms are moved into position, the upper clamp ring is moved upward to its primary stacking height with the bladder being relaxed. Then, a vacuum is applied and the bladder assembly is lowered to the bottom side wall of the tire mold. Then the vacuum is broken, and the upper clamp ring is dropped to its secondary stacking height. The stripping arms are tilted releasing the cured tire to the back of the press.
While the above steps are the typical steps involved in curing a tire using a tire curing press having a standing center post, other sequences or the omission or addition of steps are contemplated and understood to be incorporated in this disclosure.
Conventionally, a tubular, fixed height spacer is placed over the center post and rests on the center mechanism adjacent to the lower clamp ring assembly to limit the extent to which the upper clamp ring assembly drops as it moves toward the lower clamp ring assembly. "Fixed height spacer" is understood to mean a spacer that maintains is overall height throughout the curing process.
Bladders are frequently pinched during the curing process when conventional fixed height spacers are used. The dropping of the upper clamp ring assembly and applying a vacuum allows the bladder to slacken and pulls the slackened bladder inward adjacent to the exposed portion of the center post. As this occurs, the bladder can be pinched between the end of the fixed-height spacer and the upper clamp ring, thereby cutting the bladder. The bladder may also frequently be pinched if the press malfunctions or the power to the press is lost which typically results in the upper clamp ring dropping. The bladder may also be pinched if the upper clamp ring is dropped through tire curing press operator error. Over time, the bladder tends to be cut after repeated pinching causing the bladder to leak, and not to hold sufficient pressure during the tire curing process. When the bladder leaks, tires tend to be produced which have poor inside finish, poor bead formation or other defects which tend to reduce manufacturing yields and increase the number of defective tires produced. Thus, when the upper clamp ring assembly is raised and the bladder is under vacuum, a portion of the center post of the bladder assembly is exposed which allows for the bladder to be pinched.
U.S. Pat. Nos. 5,393,480 to Pizzorno, and 3,976,409 to Athey disclose conventional tire curing presses, bladder assemblies and tire curing processes and are hereby incorporated by reference. Athey '409 discloses a center mechanism for a conventional tire curing press having a single piece cylindrical sleeve supported on a ledge on the piston rod below the lower clamp ring for limiting the extent of travel of the piston rod. Pizzorno '480 discloses a locating sleeve disposed over the press drive rod between the clamp rings having a pair of semicircular elements.
A disadvantage of conventional spacers is that they tend to leave a portion of the center post exposed and allow the bladder to be pinched, or they tend to require manual adjustment to change the operating position of the upper clamp ring assembly relative to the lower clamp ring assembly.
What is desired, therefore, is a bladder assembly for a tire curing press that limits the extent to which the upper clamp ring assembly is dropped, but does not leave the center post exposed so as to allow the bladder to be pinched between the upper end of the spacer and the upper clamp ring. A spacer that substantially covers the center post of a bladder assembly so as to not leave the center post so exposed is also desired.